The objective of this study is to evaluate the efficacy of an innovative program of health behavior change in modifying the prevalence of two widespread health risk factors in work settings. The target risk factors are cigarette smoking and obesity, both of which have been linked to accute and chronic disease incidence and premature mortality. The proposed intervention consists of a comprehensive behavioral education component, offered through self-instruction or biweekly group sessions, and a motivational component, based on principles of self-reinforcement, involving a voluntary payroll withholding plan of self-selected deductions whose returns are contingent on progress toward behavior change goals. Preliminary studies in worksite populations show that the proposed intervention is attractive to employees and produces behavior change results that are superior to others reported in the literature. Thirty firms with 400 to 800 employees would be recruited for this project and randomized to treatment or no treatment. Treated firms would receive intervention for a period of 24 months. Surveys of cross-sectional and cohort samples before and after tratment would be conducted to provide information for evaluating the effects of the treatment program on smoking rates and body weight. Analyses would also examine differential effects among employee subgroups and generalization of treatment effects to behaviors not specifically targeted for change, such as quality of diet and physical activity. In addition, characteristics of worksites that facilitate or hinder program effectiveness would be explored.